Upgrade of deb packages from 10.1 to 10.2 doesn't work on Ubuntu Bionic

http://buildbot.askmonty.org/buildbot/builders/kvm-deb-bionic-amd64/builds/481/steps/upgrade2/logs/stdio

dpkg: error processing archive /tmp/apt-dpkg-install-WXuMyH/1-libmariadb3_10.2.17+maria~bionic_amd64.deb (--unpack):

 trying to overwrite '/usr/lib/mysql/plugin/dialog.so', which is also in package libmariadbclient18 1:10.1.34+maria-1~bionic

dpkg-deb: error: paste subprocess was killed by signal (Broken pipe)

To reproduce the problem, it's enough, on a clean machine where none of mariadb|mysql packages are installed:

• add official MariaDB 10.1 repo to the list (currently points at 10.1.34);
• run sudo apt-get install libmariadbclient18 (works okay);
• modify the repo list to point at the official MariaDB 10.2 repo (currently 10.2.16);
• run sudo apt-get install libmariadb3

=> it produces the error as above.

The very same sequence of actions with the same MariaDB versions works fine on Debian Stretch. I don't know what's the difference between Bionic and Stretch is.